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Per NCERT §2.6.6, the actual ground-state valence configurations of CHROMIUM (Z = 24) and COPPER (Z = 29) are which (rather than the naive Aufbau prediction)?
ACr: 3d⁵ 4s¹ and Cu: 3d¹⁰ 4s¹ — driven by extra stability of half- and fully-filled subshells
BCr: 3d⁴ 4s² and Cu: 3d⁹ 4s²
CCr: 3d⁶ and Cu: 3d¹¹
DCr: 4s² 3d⁴ and Cu: 4s² 3d⁹
Answer & Solution
Correct answer: A. Cr: 3d⁵ 4s¹ and Cu: 3d¹⁰ 4s¹ — driven by extra stability of half- and fully-filled subshells
Per NCERT §2.6.6 + Table 2.6, Cr = [Ar] 3d⁵ 4s¹; Cu = [Ar] 3d¹⁰ 4s¹. Driven by extra stability (symmetry + exchange energy) of half- / fully-filled d subshells.
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